We map the distribution and properties of the Milky Way ’ s interstellar medium as traced by diffuse interstellar bands ( DIBs ) detected in near-infrared stellar spectra from the SDSS-III/APOGEE survey .
Focusing exclusively on the strongest DIB in the H -band , at \lambda \sim 1.527 \mu { m } , we present a projected map of the DIB absorption field in the Galactic plane , using a set of about 60,000 sightlines that reach up to 15 kpc from the Sun and probe up to 30 magnitudes of visual extinction .
The strength of this DIB is linearly correlated with dust reddening over three orders of magnitude in both DIB equivalent width ( W _ { DIB } ) and extinction , with a power law index of 1.01 \pm 0.01 , a mean relationship of W _ { DIB } / A _ { V } = 0.1 Å mag ^ { -1 } and a dispersion of \sim 0.05 Å mag ^ { -1 } at extinctions characteristic of the Galactic midplane .
These properties establish this DIB as a powerful , independent probe of dust extinction over a wide range of A _ { V } values .
The subset of about 14,000 robustly detected DIB features have an exponential W _ { DIB } distribution .
We empirically determine the intrinsic rest wavelength of this transition to be \lambda _ { 0 } = 15 272.42 Å and then calculate absolute radial velocities of the carrier , which display the kinematical signature of the rotating Galactic disk .
We probe the DIB carrier distribution in three dimensions and show that it can be characterized by an exponential disk model with a scaleheight of about 100 pc and a scalelength of about 5 kpc .
Finally , we show that the DIB distribution also traces large-scale Galactic structures , including the central long bar and the warp of the outer disk .